Discharge lamp and method of manufacture



Sept. 15, 1942. N. c. BEESE DISCHARGE LAMP AND METHOD OF MANUFACTURE Filed Sept. 30, 1939 I INVENTOR 2V. BEL-25E.

mm W

ATTORNEY surface thereof has been etched,

Patented Sept. 15, 1942 Norman Pennsylvania Carl m, Verona, N. 1., asaignor to Westinghouse Electric & puny, East Pittsburgh, Pa

Manufacturing m a corporation of A Application September 30, 1939, Serial No. 297,235

6 Claims. (cuts- 122) This invention relates to discharge lamps and the method of manufacture, and more particularly to devices for eiilciently generating ultraviolet radiations.

The principm object of my invention, generally considered, is the eiilcient production of ultra-violet or other radiation by means of a discharge lamp in which the envelope thereof is either of minimum thickness, or the inner surface of which is protected from the deteriorating action of the discharge, or both.

Another object of my invention is the production of envelopes for discharge lamps, by etching the inner surface to decrease the wall thickness to such an extent that the ultra-violet radiation transmission characteristics are mate rially improved.

A further object of my invention is the production of an envelope for a discharge device having a thickness less than that to which the glass could be drawn by ordinary commercial methods.

A still further object of my invention is the production of envelopes for discharge devices in which the inner surfaces are protected from the deteriorating action of the discharge by a coating of silica applied thereto.

Other objects and advantages of the invention, relating to the particular arrangement structlon of'the various parts, will become apparent as the description proceeds.

Referring to the drawing illustrating my invention:

Figure l is a view of a lamp, embodying my elevation and partly in loninvention, partly in gitudinal section. I

Figure 2 is an enlarged cross-sectional view, on the line H-lI of Figure l, in the direction of the arrows.

Figure 3 is a fragmentary enlarged longitudinal sectional view of an envelope during the process of manufacture.

Figure 4 is a view similar to Figure 3, but showing the form of the envelope after theinner or the wall thickness otherwise decreased.

Figure 5 is a view but showing the envelope after a coating of silica has been applied thereto, a smaller discharge lamp being shown in position for testing the transmission characteristics of said envelope.

Figure 6 is an enlarged fragmentary sectional view showing the coating of silica on the inner surface of the envelope.

Figure '7 is a transverse and concorresponding to Figure 4,

envelope sucnas illustrated in Figure 3, but showing a modification.

Referring to the drawing in detail and first considering the embodiment of my invention 11- lustrated in Figures 1 to 4, inclusive, there is shown a discharge lamp ll comprising an en- 'velope I! of suitable vitreous material, such as Corning 972 high transmission ultra-violet glass, which is a. form of Corex glass.

As is well known, the effectiveness of the radiations in the ultra-violet from a discharge lamp having a vitreous or. glass envelope, is largely dependent upon the thickness of the walls of said envelope, that is, the absorption in the glass varies as a logarithmic function of the glass thickness. By decreasing the wall thickness, we can immediately increase the transmitted amount of the short wave length rays, or those which are bactericidal in character.

Fromlife test data, it has been found that there is a very large percentage loss of transmitted ultra-violet radiation during the first 25 to hours burning. This loss is due largely to solarization of the glass and is directly proportional to the wall thickness. This initial loss varies from 20 to 40% of the reading taken immediately after exhaust. To increase the initial output and; minimize the reduction caused by solarization, I propose to make the glass tubing of the minimum wall thickness that can be conveniently manufactured and still withstand operations, such as handling and shipping, and then etch out the inner surface of the envelope with hydrofluoric acid, or other material, so that the minimum useful wall thickness is obtained. Such an operation is desirable for lamps of small diameter such as /2", but is of even greater value for lamps of larger diameter. The minimum wall thickness varies, of course, with the diameter.

For the purpose of carrying out my invention, I take a piece of drawn tubing l3 of a minimum wall thickness (of say about 1 mm. for tubing having an internal diameter of about /2 inch or 1.27 cm), as above mentioned, and coat the lower end thereof, inside and out, with paraffine I4, to protect it from the action of etching fluid, and then close said lower end with a rubber cork IS. The tube I3 is then filled with etching fluid l5 up to a certain point, indicated'at ll, said fluid being desirably hydrofluoric acid; The fluid i is desirably moved during the etching process in order to avoid pitting, as by rotating the tube 13 back and forth about its axis or sectional view of an agitating. By protecting the lower end of the 2 4 'aaeaese tube by paraiiine or theilike, and the upper end It may sometimes be desirable to. take the by keeping the level at IT, I thereby provide ultra-violet radiations from 'only one side of the a tube, as shown in Figure 4, which has a minlamp, in which event a lamp having greater imum wall thickness at ll, intermediate the ends, strength, and giving all the desired output, may

which may be of the order of about one-half 54 provided by etching around only part of the that of the end portions, while said end portions circumference of the tube It. This partial etch I! are of normal wall thickness, corresponding ing may be accomplished by coating around only with the initial thickness of the glass prior to a portion of the circumference, between the etching. In this way, the electrode chambers 2i totally coated end portions, as indicated by the and 22 of the finished lamp ll, showninFigui-e 1, parafilne coating 28 shown in Figure 7. When may have thicker walls, as indicated, and be a tube it, as shownin this last figure, is thus sealed to the thickerend portions, while the coated and etched, one side only thereof, is tubular portion 22, therebetween, and through formed of minimum. thickness and the ultrawhich the radiations are emitted, is of minimum v o t rad a o s o e amp are. t e o wall thickness. to be taken from that side, while the lamp is oi maybe coated with parafllne l4, inside and out, side left of initial thickness. It will also be unlike the lower end shown in Figure 3, and the od. a the t l of Figure 7, ay be whole tube, uncorked, immersed in'a bath of used with or without the silica coating 24, deetching fluid, thereby accomplishing the reducscribed in connection w h ll s 5 end tion in thickness more quickly.. While in the Af er the tube. I! or II, has been finished, bath, the tube is desirably 'moved around, or the it has h n m r! 2 n 21 on nl etching fluid agitated, to avoid pitting. the electrodes 21 and 28 sealed to the thicker If desired, I may accomplish some of the rends l9, as illustrated most clearly in Fi ure 1- sults of my invention without any further proc- These electrode! y be Such closed in the essing of the tube. However, I prefer to protect James p -ti n, al o- 4, fi y the inner surface of the tube against deleterious 11. 1 34, and owned by the assignee of' pr action of the discharge during operation of the n pp a h lamp y so be onlamp, as by amalgamation of the mercury constluoted r se as described n 1 ppl atent with alkali and other metals that are retion; h the ien zable medium in the enduced by decomposing the inner surface of the v l pe may be a rare gaseous filling, such as 60% glass tubing by the electric discharge. neon and 40% argon. to which is added a small To overcome this latter effect, I propose coatquantity of c y n o de to increase the ining the inner surface of thetube It with pure nsity of the ultra-violet radiation, he pressure silica, as illustrated in Figurei, so that the mer- 35 of e m i m being desirably about 8 mm. The cury vapor and the gaseous discharge do not envelope y e e a sted and filled in the concome indirect contact with the main or basic Vehtlohal manner, and released o li the p. content of the glass tubing, as it is known, that indicated at The lamp is a y fintack the walls of a quartz or pure silica tube as it 0 to the ends, W h p a in electrical cono one formed 0f glass, Th coating :4 of nection with the respective electrodes 21 and 28. silica may be applied in any desired manner, as Flom the foregoing d s osure. it will be seen by flushing with a mixture comprising 25% ethyl that I have devised d o arge lamp p c a silicate and 75% ethyl alcohol. Several such y ap e for eflloiently at ng tra-violet applications are desirable to form a more or less radiations, and especially t o in e ne ghborimpervious layer of silica on the inside of the hood of the mercury lines b ween 2530 and 2540 lamp envelope. A. U., said generator being especially efilcient be- Although t. i preferred t apply th silica cause of its reduction in wall thickness by etchcoating 24 to an envelope, the thickness of which n and/or the pr ion of the inner surface of has been reduced to a minimum by etching as the envelope y p o Although particupreviously described, yet some of the advantages ar adap d f r a at rad ation s nof my invention are obtainable by applying the the employment of a S ca coating is lsesilica coating to the inside surface of an envelope fl-ll on the pe of l orescent lumiline which has not been etched, as said envelope is lempsthereby protected from blackening by decom- Altholwh preferred embodiments o y nv nposition and amalgamation, although, of course, tloh have been disclosed. it Will be understood it does not have the high transmission characthat dificat ons may be made within the spirit teristics that are obtainable by etching, as preand Scope of the ppe ded c a ms. The embodiviously described. ments which have been disclosed are operable at The coating of silica applied to. a tube I3, 10W rent densities to p odu e a discharge p t h d unetched, is shown enlarged in Figure ticularly efi'ective for bactericidal and fungicidal 6. Figure 5 represents an envelope etched and actiohthen silica coated, being tested for its transmis- I claim! sion characteristics by having a small ultra- The method of finishing an v ope f 8- violet generator 25 inserted therein and operated, as discharge. p. mp s n ng with a and the radiations which pass through the walls ethyl Silicate m x ure o coat the inner surface thereof tested for the intensity of the ultra-violet thereof with Silica and protect It nst ecomrtio 1 position during operation. V

.It will also be understood that if I desire A dlsoherge p comprising an elongated erely to construct an envelope without applyenvelope of high transmission ultra-violet glass ng the silica coating 24 to the inner surface and consisting of end chambers connected by a hereof, or unetched and with a silica coating 24, tube, the bore of said tube being smaller than uch envelopes, as respectively illustrated in Figthat of said end chambers, the thickness of the es 4 and 6, may be tested in the manner indiend chamber walls being about one millimeter, ated in connection with Figure 5. the wall of said connecting tube for substantially As an alternative, both ends of the tube I: that much reater stren th by havin the other the mercury vapor in aidischarge does not atlshed y having oonte-ot p 3| and 32 applied its entire length being etched to a thickness of about one-half. millimeter, an electrode in each end chamber, the inner surface of said connecting tube for substantially its entire length being coated with substantially pure silica to protect it against decomposition during operation of the device, and a rare gaseous filling admixed with mercury vapor enclosed in said envelope, said device being operable at low current densities to produce a discharge particularly effective for bactericidal and fungicidal purposes.

3. A discharge lamp comprising an elongated envelope of high transmission ultra-violet glass, envelope being reduced for a major portion of the distance between the ends to a thickness of one-half that of the walls of the end portions, an electrode in each end portion, the inner surface of that portion of said envelope of reduced wall thickness, being coated for substantially its entire length with substantially pure silica in protect it against decomposition during operation of the lamp, and a rare gaseous filling admixed with mercury vapor enclosed in said envelope, said lamp being operable at low current densities to produce ultra-violet radiations particularly effective for bactericidal and fungicidal purposes. 5. The method of finishing an envelope for a the order of approximately discharge lamp comprising reducing the thickness thereof by etching its inner surface for a major portion of a distance between its ends, and flushing with an ethyl silicate mixture to coat said inner surface with silica and protect it against decomposition during operation.

5. An elongated envelope of high transmission ultra-violet glass and consisting of end chambers connected by a tube, the bore of said tube being smaller than that of said end chambers, the thickness of the end chamber walls being about one millimeter, and the wall of said connecting tube for substantially its entire length being re duced to a thickness of about one-half millimeter and coated for substantially its entire length with substantially pure silica to protect it against decomposition during operation.

6; An elongated envelope of ultra-violet glass, the walls of which are reduced for a major portion of the distance between the ends to a thickness of the order of approximately one-half that of the the inner surface of that portion of said envelope of reduced wall thickness beingcoated for substantially its entire length with substantially pure silica to protect it against decomposition duringoperation.

- n w cm Bra s.

high transmission walls of the end portions," 

